Implantable medical devices are used to treat patients suffering from a variety of conditions. An example of an IMD include implantable pulse generators (e.g., a cardiac pacemaker) and implantable cardioverter-defibrillators (ICDs), which are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers, when necessary. For example, a pacemaker senses an arrhythmia, i.e., a disturbance in heart rhythm, and provides appropriate electrical stimulation pulses, at a controlled rate, to selected chambers of the heart in order to correct the arrhythmia and restore the proper heart rhythm. The types of arrhythmias that may be detected and corrected by pacemakers include bradycardias, which are unusually slow heart rates, and certain tachycardias, which are unusually fast heart rates.
Implantable cardioverter-defibrillators also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct the abnormal heart rate. In contrast to pacemakers, however, an ICD can also provide more power. This is because ICDs are designed to correct fibrillation, which is a rapid, unsynchronized quivering of one or more heart chambers, and severe tachycardia, where the heartbeats are very fast but coordinated. To correct such arrhythmias, an ICD delivers a low, moderate, or high-energy shock to the heart.
In order to perform their pacing and/or cardioverting-defibrillating functions, pacemakers and ICDs must have an energy source, e.g., a battery. An example of a prior battery is shown with reference to FIG. 1. The exploded perspective view of a prior battery solution is shown having a battery cover 10 and a headspace insulator 12 along with a battery case 14 and an electrode assembly 16. Battery cover 10 includes a feedthrough 18 through which feedthrough pin 20 is inserted. The feedthrough pin 20 is conductively insulated from the cover 10 by glass where it passes through the cover 10. The feedthrough pin 20 is generally bent to align itself with connector tabs 22 extending from electrode assembly 16. The battery cover 10 also includes a fill port 24 used to introduce an appropriate electrolyte solution after which the fill port 24 is hermetically sealed by any suitable method.
The headspace insulator 12 is generally located below battery cover 10 and above a coil insulator in the headspace above the coiled electrode assembly 16 and below the cover 10. The headspace insulator 12 is provided to electrically insulate the feedthrough pin 20 from case 14 and battery cover 10. The headspace insulator 12 forms a chamber in connection with the upper surface of the coil insulator isolating the feedthrough pin 20 and the connector tabs 22 to which it is attached.
While these prior battery solutions operate well to provide an energy source for an IMD there is room for improvement in the headspace design. Specifically, these prior solutions cannot hold the feedthrough pin in a uniform isolated location. In prior battery designs, a bend or a coil is formed in the feedthrough pin to act as a strain relief. This prevents the feedthrough pin from being in a rigid condition, such as if the pin was connected directly to a tab without a bend in the feedthrough pin. However, with a bend in the feedthrough pin there is little give to prevent any fatigue of the wire or the joint where the feedthrough pin enters the feedthrough through the glass during a shock or vibration event. Therefore, the bend acts as a cushion.
The prior headspace insulator is typically a thermoformed thin-walled plastic component. It is not precisely located with respect to other internal battery components and is susceptible to deformation during the assembly process. While this condition does not present any compromise to the intent of the headspace insulator design, it can affect manufacturing yields.
One of the variables associated with prior coiled electrode battery designs and assembly methods involves the length of the feedthrough pin between the pin-to-glass interface of the feedthrough and the pin-to-tab weld. This length is determined during the pin-to tab welding operation. Previous coiled electrode battery designs employed a “hinged” cover. The design welded the feedthrough pin to the tab(s) of one electrode of the coiled electrode assembly. The electrode assembly was then seated into the case. The cover was then seated into the case to complete the assembly. The feedthrough pin was shaped to have a coil or bend placed in the pin prior to welding the pin to the tab(s). The coil or bend in the pin was located between the glass of the feedthrough and the pin to tab weld. This coil offered strain relief to the pin, the pin-to-tab weld, and the pin-to-glass interface during electrode insertion into the case and subsequent cover insertion into the case. Due to the variations in the shape of the feedthrough pin, caused from material springiness, general handling of the pin, and the tab weld personnel, the length of the pin between the pin-to-glass interface and the pin-to-tab weld varied from one assembly to the next. This non-uniform pin length caused the case to cover insertion processing to be inconsistent.
Attempts were made to prevent the stresses on the weld by providing a coil in the feedthrough pin. However, this increased the length of the feedthrough pin, which in turn increased the resistance of the pin. This was an undesirable result as the resistance consumed power from the battery.